In industry and in hospitals, so-called general detergents make up a high percentage of total detergent consumption. Apart from bleach, general detergents contain all the ingredients necessary for optimal washing, namely surfactants, soda, silicates, triphosphates and also redeposition inhibitors, optical brighteners and others. In practice, the bleach (perborate or chlorine bleaching liquor), which is missing from this list, is separately introduced into the washing process as required. Depending on the size of the factory and on the type of washing machine, general detergents are either directly introduced into the washing process in powder form through a metering system or are first made up into so-called stock liquors and subsequently introduced into the washing process in the form of a solution. Today, the preparation of stock liquors is standard practice in large-scale operations where washing is carried out in laundries and automatic metering is virtually essential. The use of stock liquors makes the washing process much more efficient, but also presupposes considerable investment which is not practical for every factory for reasons of cost and space.
Stock liquors are understood to be aqueous solutions of the detergent powder in a concentration of normally from 5 to 15% by weight and generally of the order of 10% by weight. Stock liquors are prepared in stock liquor containers having dimensions adequate to accommodate enough stock liquor for use once or twice a day. The containers are normally able to hold from 0.5 to 2 cubic meters. A typical machine for preparing stock liquors includes a stirrer, an indirect steam-operated heating system and a pump which delivers the prepared stock liquor to the washing machine. The preparation of a 10% stock liquor is generally carried out as follows:
1. Approximately 200 liters of softened water are introduced into a vessel with a capacity of 1 cubic meter of liquid. PA0 2. The stirrer and heating system are switched on and the heating thermostat is set at approximately 40.degree. C. PA0 3. 100 kg of general detergent (for example 4.times.25 kg bags) are then rapidly introduced into the vessel with the water tap and stirrer on. PA0 4. The water tap is turned off when the 1000 liter mark is reached. PA0 5. The stirrer is kept on for about another 20 minutes, during which the temperature of the solution is generally increased to 60.degree. C. The stock liquor is then ready for use and may be introduced into the washing process by means of a metering pump. PA0 1. continuous stirring of the stock liquor, PA0 2. special pumps (for example piston displacement pumps) for pumping the stock liquor, PA0 3. special construction of the pipe system between the stock liquor container and the washing machine to prevent the insoluble builder particles from sedimenting. PA0 from about 2 to about 40, preferably from about 5 to about 15% by weight of a surfactant component composed of anionic and/or non-ionic surfactants; PA0 from about 10 to about 40, preferably from about 15 to about 25% by weight of finely particulate zeolites of the NaA or NaX type or mixtures thereof; PA0 from about 0.2 to about 2.5, preferably from about 0.5 to about 2.0% by weight of xanthan gum; PA0 from 0 to about 60, preferably from about 0.5 to about 50% by weight of one or more of water-soluble, organic or inorganic complexing agents, alkali carbonates, alkali silicates, alkali sulfates and also other standard ingredients of powder-form washing and cleaning agents; and PA0 balance to 100% by weight of free water, provided the free water content does not exceed about 20% of the weight of the preparation.
The particular demand for stock liquor is regulated through the automatically controlled washing program. The satisfactory operation of a stock liquor system of the type in question presupposes inter alia that the detergent ingredients are either completely dissolved in the solution or at least are kept finely suspended therein. Both the sedimentation of and the creaming up caused by water-insoluble constituents endanger the automatic metering system because any resulting blockage in the pipe system of the machine in which the stock liquor is prepared can give rise to considerable problems in the washing process as a whole.
In general, detergents containing small quantities of water-insoluble, very finely particulate magnesium silicate can also be made up into stock liquors. Such small quantities have clearly not been a problem since faults attributable thereto have been the exception and hence the powder-form detergents used in their make-up can be safely employed.
However, phosphates in detergents are now being blamed to an increasing extent both by experts and by the public for the eutrophication of waters and, because of this, their presence is regarded as a disadvantage. Accordingly, several substances have been proposed as substitutes for the phosphates hitherto commonly used in detergents. The most successful and widely used have clearly been sodium aluminium silicates in the form of synthetic zeolites of the NaA and NaX types, such as are described, for example, in U.S. Pat. Nos. 2,882,243 and 2,882,244.
Powder-form detergents containing phosphate substitutes of this type became known for the first time in 1974 and were described in U.S. Pat. Nos. 4,083,793 and 4,148,603. Due to the increasing importance of zeolites, the need arose to try to introduce them into detergents to be made up into stock liquors. Due to their tendency towards sedimentation, however, their use in general detergents that can be made up into stock solutions would only appear to be possible in the present state of the art under the following conditions:
Unfortunately, these requirements are satisfied in only a very few factories, so that general detergents containing necessary quantities of sodium aluminium silicate for use in stock liquors has not yet been made widely available.
U.S. Pat. No. 4,215,004 describes detergent suspensions which may also contain up to 30% by weight of sodium aluminium silicate. These stabilized suspensions contain as thickener a combination of a water-dispersible cross-linked copolymer of an acrylic acid and a polyester of a polyol on the one hand and sodium polyacrylate on the other hand. These detergent suspensions are obtained by carefully stirring the individual constituents in a certain order into water. These products are thick suspensions of relatively low water content. Unfortunately, their complicated production makes them unsuitable for use in industrial laundries because the expert is accustomed to preparing the stock liquor from a stock detergent in powder form by stirring into water and not by diluting a suspension.
Storable and pumpable suspensions of sodium aluminium silicates stabilized by the addition of a dispersant are described in numerous publications, for example in U.S. Pat. Nos. 4,072,622 and 4,169,075. These stable suspensions have a very high concentration of sodium aluminium silicate. They are used for the commercial production of detergent powders containing sodium aluminium silicate and, in that respect, are preferred to the dried sodium aluminium silicate powder.
However, the above prior art does not provide the expert with any useful information as to how to solve the problem in question here. A stock liquor is a dilute aqueous solution or suspension of a detergent, so that the known teachings on the preparation of concentrated suspensions could not readily be applied to the preparation of dilute suspensions. In fact, none of the stabilizers described for concentrated sodium aluminium silicate suspensions has proved suitable for stabilizing a stock liquor containing sodium aluminium silicate.